The fate of the photoisomers of some chlorinated cyclodienes, namely, photo-cis-chlordane, photodieldrin, and photoheptachlor in mammals and in fish and other aquatic food chain organisms will be investigated. The pathways of metabolism of these compounds in mammals and fish will involve isolation, purification, and chemical characterization of metabolites. These pathways will indicate the persistence of these photoisomers and their bioalteration products in mammals and fish. Enzyme systems responsible for the in vitro metabolism of these compounds will be characterized in fish and mammals. Species-specific differences in absorption, storage, metabolism and elimination of these photoisomers will provide information about the effects of cyclodienes and their terminal residues--the photoisomers--on human health and ecosystems.